Abstract: Recently, the photoexcited triplet state of porphyrin was proposed as a promising spin-label for pulsed dipolar electron paramagnetic resonance (EPR). Herein, we report the factors that determine the electron spin echo dephasing of the photoexcited porphyrin in a water-glycerol matrix. The electron spin relaxation of a water-soluble porphyrin was measured by Q-band EPR, and the temperature dependence and the effect of solvent deuteration on the relaxation times were studied. The phase memory relaxation rate (1/Tm) is noticeably affected by solvent nuclei and is substantially faster in protonated solvents than in deuterated solvents. The Tm is as large as 13-17 μs in deuterated solvent, potentially expanding the range of distances available for measurement by dipole spectroscopy with photoexcited porphyrin. The 1/Tm depends linearly on the degree of solvent deuteration and can be used to probe the environment of a porphyrin in or near a biopolymer, including the solvent accessibility of porphyrins used in photodynamic therapy. We characterized the noncovalent binding of porphyrin to human serum albumin (HSA) from 1/Tm and electron spin echo envelope modulation (ESEEM) and found that porphyrin is quite exposed to solvent on the surface of HSA. The 1/Tm and ESEEM are equally effective and provide complementary methods to determine the solvent accessibility of a porphyrin bound to protein or to determine the location of the porphyrin.

Cite: Sannikova N. , Timofeev I. , Bagryanskaya E. , Bowman M. , Fedin M. , Krumkacheva O.
Electron Spin Relaxation of Photoexcited Porphyrin in Water-Glycerol Glass
Molecules. 2020. V.25. N11. DOI: 10.3390/molecules25112677 WOS Scopus

Files: Full text from publisher

Dates:

Published online:

Jun 9, 2020

Identifiers:

Web of science	WOS:000553858800214
Scopus	2-s2.0-85086424057
OpenAlex	W3034828489

Altmetrics: